The invention relates to a device for inserting dowels in the area of transverse expansion joints of newly laid road surfaces.
Such devices are required for producing concrete-paved road surfaces and are frequently integrated in a slip-form paver. With the aid of slip-form pavers concrete surfaces, in particular traffic roads, are produced with continuous advance. Trucks pour fresh concrete from or with the aid of special charging devices in front of the slip-form paver. By means of distributing screws or a distributing knife the concrete is spread evenly transverse to the traveling direction. Thereafter, the concrete is compacted using shaker means and shaped with a finishing board to take the desired monolithic profile.
With the aid of a dowel placing device a plurality of dowels arranged side by side and parallel to the traveling direction at predetermined distances are placed into the still unset concrete. When the concrete has set to a certain degree, an expansion joint is produced in the concrete in the dowel area such that the road surface breaks at these places when the concrete further hardens. In this way individual separate concrete plates are produced which are connected with each other by the pressed-in dowels. This allows longitudinal expansion and fixes the level of the concrete plates.
For automated insertion of the dowels it is necessary to transport a sufficient quantity of dowels to a storage container. The dowels have to be individually transported to retainers located immediately above the road surface of fresh concrete, and the dowels from said retainers can be pressed by means of dowel placing means into the concrete down to a predetermined depth.
A known device of the generic type is described in EP 0 196 698 A1. The device for inserting dowels described therein is integrated in a slip-form paver. The dowels are located in a floorless car loader movable transversely to the traveling direction, wherein the dowels can fall from the car loader, which is open towards the bottom, into recesses of a base plate serving as smoothing board. The car loader is moved over the overall working width of the machine, until dowels are inserted into all recesses. Thereafter, the car loader returns to its initial position. When all recesses are provided with dowels, the recesses are displaced such that the dowels can fall via slots in the base plate onto the fresh concrete and can then be shaken into the concrete using two forks each.
It is a disadvantage of the known device that the car loader has only a small acceptance capacity for dowels, in particular for reasons of weight, such that a person refilling the car loader must be permanently available. Another disadvantage is that the car loader must be moved beyond the working width of the machine such that an additional free space must be kept clear beside the roadway.
From U.S. Pat. No. 5,318,377 a device for inserting dowels is known where a larger quantity of dowels are stored in two magazines from which the dowels are individually fed to a chain conveyor. The chain conveyor transports the dowels to recesses in the base plate with several dowels being temporarily stored in each recess. Then the dowels are separated again and thrown by the separation device onto the fresh concrete. It is a disadvantage of the known device that the dowels have to be alignedly placed into the magazine, which results in excessive setting-up times. Further, the configuration requiring the dowels to be separated twice is too time-consuming and thus susceptible to failure.
From EP 0 518 535 A1 a device for inserting dowels is described wherein the dowels are first laid onto a place of deposit from where they are fed to a slot comprising retaining elements. A dowel placing means then presses the dowels from the retainer into the slots and into the fresh concrete.
It is an object of the invention to further improve a device of the aforementioned type such that a large quantity of dowels can be automatically deposited without interruption of work by means of a simple construction.
The invention advantageously provides that a line conveyor device accepts separated dowels from a section of a bottom or lateral area of the storage container and feeds the dowels to the slots in the smoothing board.
The invention allows use of a large-volume storage container which can be quickly loaded in a simple manner. The large storage container allows for operation without interruption of work. The simple loading of the container reduces the setting-up times and the requirement of personnel. The device according to the invention operates fully automatically, wherein only a single transporting means consisting of the line conveyor device is needed between the storage container and the smooting board. This helps to keep the construction very simple which results in a reduced susceptibilty to failure.
Preferably, the line conveyor device comprises at least two conveyor chains extending in parallel and at a distance to each other. In this way the dowels are transported at at least two places.
The line conveyor device comprises endless elements.
A chain conveyor device comprising at least one endless chain runs synchronously and in parallel to the line conveyor device in the same traveling direction and promotes the acceptance of separated dowels by the line conveyor device.
The chain of the chain conveyor device preferably runs between the conveyor chains of the line conveyor device.
On both sides of the machine frame one dowels storage container each may be arranged, wherein the traveling direction of the line conveyor device is reversible. Since the chains can run in both directions, reversing operation is also possible during which dowels are optionally taken from either of the two storage containers. This is advantageous in particular in the case of multi-lane road surfaces since in such cases the machine can be loaded from one side only.
The bottom area and/or lateral area of the at least one storage container extend at an inclination to the raod surface. In this way the dowels can descend to the lowermost point of the storage container by gravity alone when the dowels are continuously taken from the storage container.
The chain links of the conveyor chain of the line conveyor device and the chain conveyor device consist of undercut link elements between which pockets for accepting one dowel each are formed. Said pockets are dimensioned such that they can accept dowels of different diameters. Due to the fact that undercut link elements are provided the conveyor chains can reliably retain the dowels even in vertical positions without any additional guides being necessary.
The line conveyor device can be provided with a counting device counting the number of dowels accepted by the line conveyor device and transmits a counting signal to a control device for the line conveyor device. As soon as the control device detects that a sufficient quantity of dowels for the slots in the smoothing board have been accepted, the control device can stop further acceptance of dowels. For this purpose a release device is provided at the line conveyor device, which presses the dowels from the conveyor chains back into the storage container in reaction to a signal from the control device thus disengaging the dowels from the line conveyor device and the chain conveyor device. In this way it is ensured that the line conveyor device always accepts the required quantity of dowels such that the line conveyor device can continuously circulate.
The release device preferably comprises two release plates displaceable in parallel, which press the dowels out of the acceptance area in the bottom and lateral areas.
Alternatively, the release device can comprise release plates hinged to the storage container. This offers the advantage that the actuation mechanism for the release plates can be of simple configuration.
Further, the line conveyor device may comprise a means for removing excessive dowels and replacing missing dowels. Said means ensures that the line conveyor device can run continuously.
The bottom wall of the at least one storage container can be supported on elastic buffer elements and comprise a vibration device which is designed to facilitate descending of the dowels inside the storage container and sorting them into the separation means.
The retaining device for the dowels is preferably arranged in the slots, wherein the dowels are released from the retaining device when pressure is exerted by the dowel placing device.
The width of the slots in the smoothing board can be adapted to different dowel diameters, wherein the vertical position of the retaining devices is also adjustable when the slot width is varied. This ensures that the dowels cannot protrude towards the top from the slots and cannot collide with the line conveyor device.
The retaining devices in the slots can comprise pivotable spring elements. Said spring elements release the dowels at a force exerted by the dowel placing device, which considerably exceeds the force exerted by the weight of the dowels such that the dowels can fall onto the road surface and can be immediately pressed by the dowel placing device into the road surface.
With the aid of a control cam provided at the slot and a control face provided at the retaining device the retaining devices are preferably automatically adjustable in their vertical position in dependence on the slot width. This offers the advantage that together with adjustment of the slot width the height of the retaining device is adjusted, too.
The working width of the line conveyor device and the length of the slots in the smoothing board are adjustable such that they are adaptable to dowels of different lengths. In this way the machine is not only capable of processing dowels of different diameters but also dowels of different lengths.
On the slots guiding elements adjustable in the traveling direction are arranged for horizontal and vertical guidance of the line conveyor device. Said guiding elements are adjustably arranged at the smoothing board for the purpose of adaptation to the dowel length.
The smoothing board is designed such that the mutual distance between the slots transversely to the traveling direction can also be adjusted.
The conveyor chains of the line conveyor device preferably consist of twin chains so that both ends of the dowels are guided by two conveyor chains, respectively.
It is provided that the twin chains guide the dowels at the side by the inner surface of the outer part of the twin chains, the outer part of the twin chains traveling on the guides and the inner part of the twin chains transporting the dowels.
The line conveyor device operates linearly from bottom to top along the bottom or side portions of the storage container.